Cancers of the renal cortex are known as renal cell carcinomas (RCC) and represent ~80-85% of all primary renal neoplasms. The clear cell variant comprises up to 85% of all RCCs, which are expected to result in ~64,000 new cases and ~14,000 deaths in the U.S. in 2014. Clear cell RCC is a disease that increases with age and is more common in men, and as such represents a common source of cancer-related morbidity and mortality amongst our Veterans. The disease is lethal at the advanced, metastatic stage. Although several novel treatments, including small molecule tyrosine kinase inhibitors and rapamycin analogs, have received regulatory approval, their overall impact on survival is modest, and median survival for patients with metastatic clear cell RCC remains at only ~24 months. The molecular hallmark of hereditary and sporadic clear cell RCC is the biallelic inactivation of the vonHippel-Lindau (VHL) tumor suppressor gene, which is most well characterized for its role as the substrate recognition unit of an E3 ubiquitin ligase that targets hypoxia-inducible factor alpha (HIF?) for proteasomemediated degradation. Importantly, upwards of 90% of sporadic cases of clear cell RCC manifest VHL inactivation. Although restoration of the expression pVHL, the protein product of the VHL gene, suppresses tumorigenesis as does inhibition of HIF? expression, gene replacement therapy and the development of small molecule inhibitors of transcription factors such as HIF? s not readily feasible for clinical translation. The overarching goal of our proposed research is to validate HIF?-independent effects of VHL loss as viable therapeutic targets for clear cell RCC. Specifically, we propose to generate the pre-clinical data to establish that a MAP kinase kinase kinase known as transforming growth factor ? activated kinase (TAK1), which is hyperactivated in response to pVHL deficiency, is a suitable target for drug development and translation into the clinic. We have already established that TAK1 drives the activation of the c-Jun N-terminal kinase (JNK) and nuclear factor kappa B (NF-?B) pathways, both of which are pro-tumorigenic and constitutively activated in pVHL-deficient RCCs. Thus, our hypothesis is that TAK1 inhibition represents a potential therapeutic target that mediates renal oncogenesis through downstream activation of the NF-?B and JNK pathways. Based on this background and our preliminary studies, many of which have been published, we have proposed three aims: Aim 1. To establish that TAK1 inhibition prevents and retards the growth of pVHL-deficient RCCs in vitro and in vivo. Aim 2. To elucidate the underlying molecular mechanisms that are permissive for concurrent, constitutive activation of the NF-?B and JNK pathways in pVHL-deficient cells. Based on preliminary studies, we postulate that molecular adaptations acquired by pVHL-deficient RCCs are critical to the ongoing, constitutive JNK activation that characterizes pVHL-deficient cells. Aim 3. To establish that constitutive TAK1 and concurrent NF-?B and JNK activation occur in clear cell RCC patient specimens. As a critical component to the process of pre-clinical validation of a molecular target, it is vital to confirm that the relevant pathways ar indeed activated in patient specimens in a fashion that is consistent with our pre-clinical models. Successful execution of the proposed aims will lay the groundwork for the validation of TAK1, a druggable kinase that is hyperactivated as a consequence of VHL loss, as a molecular target for clinical development. In this fashion, our long-term goal is to translate our findings to the management of advanced clear cell RCC, a relatively common malignancy amongst our Veterans.